This invention relates to a lithographic printing plate precursor. More specifically, it relates to a lithographic printing plate precursor providing a lithographic plate whereby a large number of copies having clear images without any background stain can be obtained in multiset printing, in particular, a lithographic printing plate precursor of direct draw type.
Examples of lithographic printing plate precursor employed today mainly in the field of rough printing include (1) a printing plate precursor having a hydrophilic image receiving layer formed on a waterproof substrate; (2) a printing plate prepared by using a printing plate precursor having a (lipophilic) image receiving layer containing zinc oxide on a waterproof substrate, making a plate by directly drawing an image thereon and then treating the non-image part with a solution of making oil-insensitive; (3) a printing plate prepared by using, as a printing plate precursor, an electron photographic sensitive material having a photoconductive layer containing photoconductive zinc oxide on a waterproof substrate, forming an image thereon and then treating the non-image part with a solution of making oil-insensitive; (4) a printing plate precursor of silver photography type having a silver halide emulsion layer formed on a waterproof substrate, etc.
With the recent development of office instruments and advances in office automation, it has been required in the field of printing to develop an offset lithography system whereby a printing plate can be directly formed by the plate-making (i.e., image-forming) procedure using a lithographic printing plate precursor as described in the above (1) with various printers such as an electron photographic printer, a thermal transfer printer or an inkjet printer without resort to any specific treatment for making a printing plate.
Conventional lithographic printing plate precursors have surface layers serving as an image receiving layer on both faces of a substrate (paper, etc.) mediated by back face layers and intermediate layers. The back face layers or the intermediate layers are made up of a water soluble resin such as PVA or starch, a water dispersible resin such as a synthetic resin emulsion and a pigment. The image receiving layers are usually made up of an inorganic filler, a water soluble resin and a waterproofing agent.
Examples of the inorganic pigment include kaolin, clay, talc, calcium carbonate, silica, titanium oxide, zinc oxide, barium sulfate and alumina.
Examples of the water soluble resin include polyvinyl alcohol (PVA), modified PVA such as carboxy PVA, starch and its derivatives, cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose, casein, gelatin, polyvinylpyrrolidone, vinyl acetate-crotonic acid copolymer and styrene-maleic acid copolymer.
Examples of the waterproofing agent include glyoxal, aminoplast precondensates such as melamine formaldehyde resin and urea formaldehyde resin, modified polyamide resins such as methylol polyamide resin, polyamide/polyamine/epichlorohydrin adduct, polyamide epichlorohydrin resin and modified polyamide polyimide resin.
In addition, it is known that crosslinking catalysts such as ammonium chloride and silane coupling agents can be used together with these components.
Studies have been further made to improve the hydrophilicity of non-image parts, enhance the film strength of the image receiving layer and improve the printing tolerance by using, as a binder to be used in the image receiving layer of lithographic printing plate precursor, a preliminarily crosslinked resin having a functional group capable of providing a carboxyl, hydroxyl, thiol, amino, sulfo or phosphono group upon decomposition and another functional group hardening upon exposure to heat/light (Japanese Patent Laid-Open No. 226394/1989, Japanese Patent Laid-Open No. 269593/1989 and Japanese Patent Laid-Open No. 288488/1989), a combination of a resin containing the above-described functional group and a heat/light-hardening resin (Japanese Patent Laid-Open No. 266546/1989, Japanese Patent Laid-Open No. 275191/1989 and Japanese Patent Laid-Open No. 309068/1989), or a combination of a resin containing the above-described functional group with a crosslinking agent (Japanese Patent Laid-Open No. 267093/1989, Japanese Patent Laid-Open No. 271292/1989 and Japanese Patent Laid-Open No. 309067/1989).
Also, studies have been made to improve the hydrophilicity of non-image parts by using, together with an inorganic filler and a binder in the image receiving layer, resin particles containing a hydrophilic group such as a phosphono group and having a small particle diameter of 1 xcexcm or less (Japanese Patent Laid-Open No. 201387/1992 and Japanese Patent Laid-Open No. 223196/1992) or resin particles containing a functional group capable of providing such a hydrophilic group as described above upon decomposition and having a small particle diameter (Japanese Patent Laid-Open No. 319491/1992, Japanese Patent Laid-Open No. 353495/1992, Japanese Patent Laid-Open No. 119545/1993, Japanese Patent Laid-Open No. 58071/1993 and Japanese Patent Laid-Open No. 69684/1993).
However, the conventional printing plates thus obtained suffer from a problem. That is to say, in case of adding a waterproofing agent in an increased amount to improve the printing durability or using a waterproof resin to elevate the hydrophobicity, the printing tolerance can be improved but the hydrophilicity is worsened thereby causing printing stains, or in case of improving the hydrophilicity, the printing tolerance is worsened.
Under working conditions at a high temperature of 30xc2x0 C. or above, in particular, there arises a problem that the surface layer is dissolved in dampening water employed in offset printing, which causes worsening in the printing tolerance, occurrence of printing stains, etc. Concerning a lithographic printing plate precursor of direct draw type wherein an image is drawn on the image receiving layer with the use of an oil-base ink etc., there still remains an unsolved problem. Namely, when the adhesiveness between the image receiving layer of the printing plate precursor and the oil-base ink is insufficient, drop-off of the oil-base ink arises in the step of printing and thus the printing tolerance is lowered even though the non-image parts have a sufficient hydrophilicity and thus causes no printing stain as described above.
On the other hand, there has been known a plate having as the image receiving layer a hydrophilic layer containing titanium oxide, polyvinyl alcohol and hydrolyzed tetramethoxysilane or tetraethoxysilane (Japanese Patent Laid-Open No. 42679/1991, Japanese Patent Laid-Open No. 268583/1998, etc.). When this plate is employed as a printing plate in practice, however, the obtained image shows only an insufficient printing durability.
As discussed above, it has been understood that the hydrophilicity of the image receiving layer can be enhanced by elevating the moisture retention in the image receiving layer. In the conventional image receiving layers, however, an increase in the moisture retention brings about some problems such that the swelling properties of a film are enlarged and thus the film structure is weakened or the film strength is lowered, or the adhesiveness between the substrate and the image receiving layer is worsened.
The present invention aims at solving the above-described problems encountering in the conventional lithographic printing plate precursor.
Accordingly, it is an object of the present invention to provide a lithographic printing plate precursor which is excellent as an offset printing plate free from not only uniform background stains but also spotty stains.
It is another object of the present invention to provide a lithographic printing plate precursor capable of providing a printing plate whereby a large number of copies having a clear image without any drop-off, distortion, etc. can be obtained.
The above-described object can be achieved by the following constitutions (items 1 to 10).
1. A lithographic printing plate precursor comprising an image receiving layer and a waterproof substrate, wherein the image receiving layer comprises:
needle filler particles; and
a binder resin comprising a complex of: a resin comprising a bond whereby at least one of a metal atom and a semimetal atom are bonded via an oxygen atom; with a polymer compound represented by the following formula (I): 
wherein R1, R2, R3 and R4 each independently represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms; m is 0, 1 or 2; n is an integer of from 1 to 8; L represents a single bond or an organic linking group; and Y represents xe2x80x94NHCOR5, xe2x80x94CONH2, xe2x80x94CON(R5)2, xe2x80x94COR5, xe2x80x94OH, xe2x80x94CO2M or xe2x80x94SO3M wherein R5 represents an alkyl group having 1 to 8 carbon atoms, and M represents a hydrogen atom, an alkali metal, alkaline earth metal or an onium.
2. A lithographic printing plate precursor comprising an image receiving layer and a waterproof substrate, wherein the image receiving layer comprises:
porous filler particles; and
a binder resin comprising a complex of: a resin comprising a bond whereby at least one of a metal atom and a semimetal atom are bonded via an oxygen atom; with a polymer compound represented by the following formula (I): 
wherein R1, R2, R3 and R4 each independently represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms; m is 0, 1 or 2; n is an integer of from 1 to 8; L represents a single bond or an organic linking group; and Y represents xe2x80x94NHCOR5, xe2x80x94CONH2, xe2x80x94CON(R5)2, xe2x80x94COR5, xe2x80x94OH, xe2x80x94CO2M or xe2x80x94SO3M wherein R5 represents an alkyl group having 1 to 8 carbon atoms, and M represents a hydrogen atom, an alkali metal, an alkaline earth metal or an onium.
3. The lithographic printing plate precursor according to item 1, wherein the porous filler particles have an average diameter of 3 xcexcm or less and an average length of 100 xcexcm or less.
4. The lithographic printing plate precursor according to item 1 or 3, wherein a content of the needle filler particles is 25% by weight or more to that of all fillers contained in the image receiving layer.
5. The lithographic printing plate precursor according to any one of items 1, 3 and 4, wherein a mixing ratio by weight of the binder resin to all fillers in the image receiving layer is from 80:20 to 5:95.
6. The lithographic printing plate precursor according to any one of items 1 and 3 to 5, wherein the resin comprising the bond is a polymer obtained by hydrolytic cocondensation of at least one compound represented by the following formula (II):
(R10)xM10(G)z-xxe2x80x83xe2x80x83(II)
wherein R10 represents a hydrogen atom, a hydrocarbon group or a heterocyclic group; G represents a reactive group; M10 represents a 3- to 6-valent metal or semimetal; z represents a valency of metal or semimetal represented by M10; and x is 0, 1, 2, 3 or 4, provided that z-x is 2 or more.
7. The lithographic printing plate precursor according to item 2, wherein an average pore diameter of the porous filler is from 1 xc3x85 to 1 xcexcm.
8. The lithographic printing plate precursor according to item 2 or 7, wherein an average specific surface area of the porous filler is from 0.05 m2/g to 5000 m2/g.
9. The lithographic printing plate precursor according to any one of items 2, 7 an 8, wherein a mixing ratio by weight of the binder resin to all fillers in the image receiving layer is from 80:20 to 5:95.
10. The lithographic printing plate precursor according to any one of items 2 and 7-9, wherein the resin comprising the bond is a polymer obtained by hydrolytic cocondensation of at least one compound represented by the following formula (II):
(R10)xM10(G)z-xxe2x80x83xe2x80x83(II)
wherein R10 represents a hydrogen atom, a hydrocarbon group or a heterocyclic group; G represents a reactive group; M10 represents a 3- to 6-valent metal or semimetal; z represents a valency of metal or semimetal represented by M10; and x is 0, 1, 2, 3 or 4, provided that z-x is 2 or more.
A large characteristic of the present invention resides in using, as a binder resin, a complex (which will be hereinafter referred to as an xe2x80x9corganic/inorganic complexxe2x80x9d or merely a xe2x80x9ccomplexxe2x80x9d) of a resin having a bond whereby a metal atom and/or a semimetal (which will be sometimes referred to as a xe2x80x9c(semi)metalxe2x80x9d hereinafter) atom are bonded via an oxygen atom with a polymer compound represented by the above-described formula (I). Thus, the moisture retention of the image receiving layer can be considerably elevated without worsening the printing tolerance.